Conventionally, in an image forming unit in an image forming device, such as an electrographic printer or photocopier, in order to stably charge the surface of a photosensitive drum, minute voids are formed between the surface of the charge roller and the surface of the photosensitive drum by covering an outer circumferential surface of the charge roller with a semi-conductive resin coat layer containing particles of magnesium oxide, which is an electric insulator, with a particle size (or average particle diameter) of 15 μm-50 μm. The outer circumferential surface of the charge roller has asperity, or roughness, due to the particles of magnesium oxide. Such technology is described in Japanese laid-open application publication number 2000-75701.
However, in the conventional image forming unit, when this unit is left idle for a long time, deformation marks occur on an area of contact between the charge roller and the photosensitive drum, which may cause deterioration of image quality. The objective of the present invention is to improve the image quality.